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Full text of "Electrophoretic studies of turbidity removal by coagulation with ferric sulfate"

ELECTROPHORETIC STUDIES OF 
| TURBIDITY REMOVAL BY COAGULATION 

2 WITH FERRIC SULFATE 



By 
JAMES VERNON WALTERS 






A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF 

THE UNIVERSITY OF FLORIDA 

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE 

DEGREE OF DOCTOR OF PHILOSOPHY 



UNIVERSITY OF FLORIDA 

August, 1963 



ACKNOWLEDCMENTS 

The author wishes to express his gratitude to his committee 
chairman, Dr. A. P. Black, for guidance and encouragement he has given 
during the investigation and for his generosity in the giving of him- 
self to his students. He deeply appreciates the friendship and help- 
fulness of Prof. J. E. Kiker, Jr., Prof. G. B. Morgan, Jr., and Prof. 
T. deS. Furraan, members of his supervisory committee, •who have helped 
him in many ways during his graduate study at the University of Florida. 
Dr. T. R. Waldo, of his supervisory committee, has generously given her 
time to guide the author in his dissertation preparation. He gratefully 
acknowledges his indebtedness to her. 

Dr. Korihito Tanbo's sketch of the Brig'gs cell which is included 
herein, will remind the author of the hours of consultation Dr. Tanbo 
gave him. Mrs. A. L. Smith, Dr. R. F. Chris tman, and Dr. S. A. Hannah 
have also given the author the advantage of their experiences in water 
coagulation research. The author thanks Mrs. J. G. Larson, Mr. W. T. 
Walters, and Mr. C. Chen for their help in the execution and reporting 
of his experiments. 

The research was directly supported by Water Supply and Pollution 
Control Research Grant WP-139 from the Public Health Service, and was 
indirectly supported by Ford Foundation loans and Public Health Service 
Traineeships which financed the author's graduate study. 



ii 



The author shall forevermore try to express his appreciation and 
gratefulness to his sons and his wife, Barbara, whose love and under- 
standing have sustained him. 






Xi_ 



CONTENTS 

Page 

ACKNOWLEDGMENTS ......... i 1 

LIST OF TABLES . ^- 

LIST OF FIGURES • . . . • . . • • vii 

CHAPTER 

I. INTRODUCTION . . . . 1 

II. HISTORICAL REVIEW 3 

III. COAGULATION THEORY . * I 1 

IV. PURPOSE AND SCOPE ......... . 24 

V. EXPERIMENTAL MATERIALS AND PROCEDURES ....... 26 



25 
26 
26 



Materials .«.»..»•««»»»»»«»••« 
Clays »«»»»»••••»•«•••»•••• 
Ferric Sulfate »•»•••»»•»•••♦••• 

Procedures «♦•♦••••»••••••••*** 2o 

Preparation of Clay Suspensions • ••••••« 28 

Preparation of Ferric Sulfate ......... 29 

Coagulation Tests • ••*•*•*.•••»*« 3^ 

Saraple Preparation • •••«•••*«•••« 3^ 

Flocculation «»•♦•»••••••••••• 5— 

Initial and Residual Turbidity Measurements • 3 2 

Residual Iron Determinations * 32 

i Measurement ofpH .............. 33 

Electrophoretic Mobility Determinations 33 

Dosing and Mixing ......... 33 

Conductance Measurement ........... 3"^ 

Measurement of pH * In 

Particle Mobility Measurement ........ 3^ 

VI. DISCUSSION OF RESULTS 3S 

VII. CONCLUSIONS • 76 

APPENDIX ..........*..».....*♦•••••• 7b 



xv 



Page 

BIBLIOGRAPHY • • • 102 

BIOGRAPHICAL SKETCH • • 1°? 















LIST OF TABLES 

Table Page 

1. Analysis of Ferric Sulfate Used for Coagulation ... 27 

2 . Properties of the Clay Suspensions 38 

3. Coagulant Dosages 39 

if-. Effect of pH on Electrophoretic Mobility and 

Sedimentation of Montraorillonite Clay ........ 79 

5. Coagulation of Montraorillonite Clay With 3.0 
Milligrams Per Liter of Ferric Sulfate 80 

6. Coagulation of Montraorillonite Clay With 5.0 
Milligrams Per Liter of Ferric Sulfate 83 

7. Coagulation of Montraorillonite Clay With 50 
Milligrams Per Liter of Ferric Sulfate ....... 85 

8. Effect of pH on Electrophoretic Mobility and 
Sedimentation of Fuller's Earth ........... 87 

9. Coagulation of Fuller's Earth With 3.0 Milligrams 
Per Liter of Ferric Sulfate 89 

10. Coagulation of Fuller's Earth With 5.0 Milligrams 
Per Liter of Ferric Sulfate 91 

11. Coagulation of Fuller's Earth With 50 Milligrams 
Per Liter of Ferric Sulfate . 93 

12. Effect of pH on Electrophoretic Mobility and 
Sedimentation of Kaolinite Clay ..... 94 

13. Coagulation of Kaolinite Clay With 3.0 Milligrams 

Per Liter of Ferric Sulfate ...... 95 

1+. Coagulation of Kaolinite Clay With 5.0 Milligrams 

Per Liter of Ferric Sulfate 97 

15. Coagulation of Kaolinite Clay With 50 Milligrams 

Per Liter of Ferric Sulfate 100 



vi 






LIST OF FIGURES 

Figure Page 

1. The Helmholtz Layer Model 16 

2. The Gouy-Chapman Diffuse Layer Model. . 18 

3. The Stern Layer Model 20 

4. The Briggs Cell 35 

5. The Effect of pH and Mobility upon Coagulation. Clay: 
Montmorillonite Ferric Sulfate Dosage: 0.0 mg/l .... 42 

6. The Effect of pH and Mobility upon Coagulation. Clay: 
Montmorillonite Ferric Sulfate Dosage: J.O mg/l . . . „ 44 

7. The Effect of pH and Mobility upon Coagulation. Clay: 
Mofttmoriilsilit*! Ferris Sulfate BoSsg^J $*Q Fig/l . , , , 45 

8. The Effect of pH and Mobility upon Coagulation. Clay: 
Montmorillonite Ferric Sulfate Dosage: 50. mg/l .... 46 

9. The Effect of pH and Mobility upon Coagulation. 

Clay: Montmorillonite 48 

10. The Effect of pH and Mobility upon Coagulation. Clay: 
Fuller's Earth Ferric Sulfate Dosage: 0.0 mg/l .... 49 

11. The Effect of pH and Mobility upon Coagulation. Clay: 
Fuller's Earth Ferric Sulfate Dosage: 3.0 mg/l .... 50 

12. The Effect of pH and Mobility upon Coagulation. Clay: 
Fuller's Earth Ferric Sulfate Dosage: 5-0 mg/l .... 52 

13. The Effect of pH and Mobility upon Coagulation. Clay: 
Fuller's Earth Ferric Sulfate Dosage: 50. mg/l .... 53 

14. The Effect of pH and Mobility upon Coagulation. Clay: 
Fuller's Earth 54 

15. The Effect of pH and Mobility upon Coagulation. Clay: 
Kaolinlte Ferric Sulfate Dosage: 0.0 mg/l 55 

16. The Effect of pH and Mobility upon Coagulation. Clay: 
Kaolinite Ferric Sulfate Dosage: 3 .0 mg/l ^G 



vii 






Figure P age 

17. The Effect of pH and Mobility upon Coagulation. Clay: 
Kaolinite Ferric Sulfate Dosage: 5.0 mg/l 57 

18. The Effect of pH and Mobility upon Coagulation. Clay: 
Kaolinite Ferric Sulfate Dosage: 50. mg/l 58 

19. The Effect of pH and Mobility upon Coagulation. 
Clay: Kaolinite 59 

20. The Effect of pH on Iron Residual. Clay: Montmorillonite 
Ferric Sulfate Dosage: 3.0 mg/l 61 

21. The Effect of pH on Iron Residual. Clay: Montmorillonite 
Ferric Sulfate Dosage: 5.0 mg/l 62 

22. The Effect of pH on Iron Residual. Clay: Montmorillonite 
Ferric Sulfate Dosage: 50. mg/l ..... 63 

23. The Effect of pH on Iron Residual. Clay: Fuller's Earth 
Ferric Sulfate Dosage: 3.0 mg/l Sk 

ZUr. The Effect of pH on Iron Residual, Clay: Fuller's Earth 

Ferrie Sulfate Dosages 5.0 mg/l .,..,,,, 65 

25. The Effect of pH on Iron Residual. Clay: Fuller 3 s Earth 
Ferric Sulfate Dosage: 50. mg/l ............. 66 

26. The Effect of pH on Iron Residual. Clay: Kaolinite 

Ferric Sulfate Dosage: 3.0 mg/l 6? 

2?. The Effect of pH on Iron Residual. Clay: Kaolinite 

Ferric Sulfate Dosage: 5.0 mg/l ............. 68 

23. The Effect of pH en Iron Residual. Clay: Kaolinite 

Ferric Sulfate Dosage: 50. mg/l ..... 69 

29. Quantities of Acid or Base Required for pH Adjustment 

of Fuller's Earth ............. 71 

30. Quantities of Acid or Base Required for pH Adjustment 

of Fuller's Earth 72 



ly 



31. Quantities of Acid or Base Required for pH Adjustmen 
of Fuller's Earth ....... ... 73 

32. Quantities of Acid or Base Required for pH Adjustment 

of Fuller's Earth 74 

33. Quantities of Acid or Base Required for pH Adjustment 

of Fuller's Earth • . . 75 



sail 



I. INTRODUCTION 

Clays are the most common source of turbidity in surface -waters 
used for municipal and industrial water supplies. Before surface water 
is satisfactory for domestic and industrial use, most of the clay and 
other particulate matter present in the water must be removed. Removal 
of the suspended matter is usually accomplished by alum or ferric sul- 
fate coagulation, sedimentation, and rapid sand filtration. Water 
treatment plants which utilize this process produce finished waters 
which regularly exceed the minimum quality required for potable water 
by the U. S. Public Health Service. 1 ' 2 ' 3 The specific Public Health 
Service recommendation concerning turbidity is that the turbidity of 
drinking water be less than five units. 

Prediction of the optimum coagulation conditions for the produc- 
tion of such high quality water from a given raw water is very diffi- 
cult. In the absence of records of previous treatment of water from 
the same source it is rationally impossible at present. The difficulty 
of coagulation prognosis is the result of complexly related effects of 
the numerous properties of the raw water and the chosen coagulation 
conditions which affect the efficacy of coagulation. Among these con- 
ditions and properties are: specific coagulant chosen; coagulant dosage; 
pH, alkalinity, ionic constituents, and base exchange capacity of the 
raw water; and size, shape, chemical nature, hydration, and charge of 
the colloidal particles in suspension. Most of the factors which affect 
coagulation also affect the electrophoretic mobility of the suspended 

- 1 - 






- 2 - 

colloidal particles. 

Electrophoresis is the movement of electrically charged particles, 
suspended in a conducting liquid medium, which results from the impres- 
sion of an electric field. Electrophoretic mobility is the ratio of 
the speed of electrophoretic movement to the intensity of the elec- 
trical field which produced the motion. It is commonly expressed in 
microns per second per volt per centimeter. 

Mineral content, coagulant, coagulant dose, alkalinity and 
nature of clay particles, of the numerous parameters which affect elec- 
trophoretic mobility and coagulation, can be chosen and controlled for 
a selected synthetic clay .suspension. In addition to these parameters 
which can be selected, pH, base exchange capacity, effectiveness of 
coagulation and particulate electrophoretic mobility for a given suspen- 
sion can be directly measured. 

The present research has been performed in order to study the 
empirical relationships among electrophoretic mobility, residual tur- 
bidity, coagulant dosage, and residual iron (the mensurable parameter) 
for the ferric sulfate coagulation of suspensions of three different 
clays over the pH range between three and ten. To my knowledge, such 
a study has not been attempted before. The relationships discovered 
are described herein, and the effectiveness of ferric sulfate coagula- 
tion of these clays is compared with that of. their alum coagulation, 
reported earlier by Black and Hannah. 









II. HISTORICAL REVIEW 

The earliest records of the coagulation process have been traced 
by Black who "wrote: 

Although various crude methods of water purification, generally ,< 
characterized as coagulation , have been knot-in and used since J ' 
ancient times , knowledge of the fundamental factors involved in 
the process has been acquired comparatively recently. 

The earliest references of scientific interest in coagulation as a 

process for the treatment of water are references to the works of 

D'Arcet ^ and Jeunet. ' D'Arcet at the beginning of the nineteenth 

century and Jeunet in 1865 sought to establish the value of the process, 

but it was not used for the treatment of a public water supply until 

1881, After its initiation in Bolton, England* the process was soon 

adopted in Holland and in the United States. 

The first coagulation patent was granted , in 1884 , to Isaiah 
Smith Hyatt. 5 Following the suggestion of Col. L. E. Gardner, Superin- 
tendent of the Hew Orleans Water Company, Hyatt successfully treated 
turbid water by combining the use of perchloride of iron as a coagu- 
lant with his process of rapid filtration. His patent covered not only 
the use of perchloride of iron, but also of "any other suitable agent 
•which is capable of coagulating the impurities of the liquid and pre- 
venting their passage through the filter bed." 

The 1884 Annual Report of the State Geologist of New Jersey con- 
tained results of tests of various salts as coagulants. Austen and 
Wilber 6 ' 9 concluded that of the salts investigated, aluminum sulfate 
was most effective. Fuller 10 published a description of similar studies 

- 3 - 












_ h f - 
in 1898. He found sulfates of iron and aluminum to be most effective. 
The chloride of these elements followed next in order, but their use as 
coagulants in water treatment has not developed on a practical scale. 

In the year of Fuller's publication, ¥, B. Bull, 5 at Quincy, 
Illinois, began using a mixture of ferrous sulfate and lime for coagu- 
lation. Fourteen years later, E. V. Bull reported the first use of 

chlorinated copperas. This chemical was not tried again until 1928, 

12 
when Hedgepeth and Olsen used it for the successful treatment of a 

highly colored water. Ferric ion was produced by oxidation of the 
ferrous sulfate with chlorine. 

As use of the process has become prevalent, the number of re- 
searchers and the scientific disciplines they represent have prolif- 
erated. Black ^ and Packham in recent reviews of coagulation theory 
and related literature, thoroughly cover the many facets of historical 
and contemporary research, theory, and practice. The literature cited 
in the present study will consequently be limited to that directly 
related to the research herein reported. 

In 1923 the first of a series of studies by Theriault, Clark, 

14 
and Jdiller was reported. The paper by Theriault and Clark described 

their treatment of several buffered solutions with various amounts of 

alum to determine the effect of pH upon the rate of floe formation. 

They assumed that the optimum pH for coagulative treatment of water 

would be the pH at which the minimum time was required for the formation 

of the aluminum floe. They found that generally the best floe formation 

occurred in the pH range 4.95 to 5»40. Higher alum doses resulted in 

broader ranges of pH over which rapid coagulation was observed. These 

workers were unable to explain the difference between values of pH 



- 5 - 

which accompanied rapid coagulation in their study and the higher values 
; .. observed to be most effective in water treatment plants. 

In the same year, Baylis, using alum to coagulate natural 
waters of varying alkalinity, noted that for a given pH, waters of 
higher alkalinity required larger quantities of coagulant to accomplish 
satisfactory treatment. For any chosen water he was able to reduce the 
alum dosage by adjusting the pH with a strong acid, thereby neutral- 
izing a portion of the alkalinity originally present. The values of pH 
for optimum coagulation were in the range 5*5 to 7.0. 

Late in 1923, Miller published the second of the Theriault, 
Clark, and Miller papers. ■ He described their constituent study of pre- 
cipitates formed by the mixing of potassium alum solutions with sodium 
hydroxide solutions of various molarities. Although the anion concen- 
tration of the coagulant had no practical effect, the amount of alkali 
mixed with a given quantity of aluminum exerted considerable influence 
upon the composition of the precipitate. The ratio of aluminum to sul- 
fate ion was determined for the floe over the useful pH range, but the 
exact chemical nature of the floe was not determined. His review of 
treatment plant records revealed that optimum coagulation occurred 
within the pH range 5.4 to 8.5. 

In another series of tests (1925) Miller ' investigated the 
effects of various anions upon the formation of floe in solutions of 
potassium alum. Generally, the anions of higher valence exerted 
greater influence upon coagulation, and'less alkali was necessary in 
their presence* 

The composition of precipitates from ferrous and ferric salt 
solutions was the subject of another 1925 publication by Miller. 






- 6 - 

There precipitates from the iron salts were found to be very similar to 
floe from the analogous aluminum salts, except that they were formed at 
pH values significantly lower than the minimum pH values observed for 
alum floe and that they remain insoluble above the maximum pH at which 
alum floe exists. 

The results of Miller's experimental work allowed him to make 
three statements concerning the optimum conditions for floe formation 
with both iron and aluminum coagulants, (l) There must be present in 
the water a certain minimum quantity of the met alli c coagulant ion. 
. (2) There must be present an anion of strong coagulating power such as 
the sulfate ion. (3) The pH must be properly adjusted. 

In 1928 Bartow and Peterson 9 examined the effects of various 
salts upon the formation rate for alum floe over the useful pH range. 
Many of the salts studied increased slightly the rate of floe formation 
■ and extended, on the acid side, the pH range over which floe occurred. 

In a paper published in 1928 and now regarded as a classic in its 

20 
field, Mattson described the coagulation of clay suspensions and the 

electrophoretic mobility measurement of clay particles as mobility was 

altered by various dosages of aluminum salts. His work demonstrated 

the effect of the different anions and cations upon particle charge. He 

specifically predicted the utility of electrophoretic studies in water 

coagulation investigations and pointed out the predominant role played 

by the hydrated oxides formed during coagulation. 

In three articles Black and others 21 » 22 » 2 3 report investigations, 

made on a laboratory and semi-plant scale, of the effects of several 

anions upon the rate of floe formation for both aluminum and ferric 

salts. They proposed improved conditions for laboratory study of 






- 7 - 

coagulation. Also they recommended the use of larger samples and con- 
tainerss, constant stirrings and isohydric indicators. With such im- 
provements they could duplicate pilot plant results. Anions were found 
to be useful to increase the rate of coagulation and to broaden the pH 
ranges of rapid floe formation. The pH range for floe formation was 
wider for ferric sulfate than for alum, but no iron floe formed between 
pH values 6,5 and 8.5. The authors stressed the importance of adsorp- 
tion as an important mechanism of turbidity removal and also attributed 
zones of no floe formation to a change in particle charge. 

In the slightly more than a decade since the publication of 
Black's 193^ article, the interest of water chemists seem to have been 
focused upon activated silica and other coagulant aids. The work of 

Oh. O C 

Langelier and Ludwig * ? marked the return of many researchers to the 
field of basic coagulation theory. They initiated the use of synthetic 
clay suspensions and called attention to the importance of base exchange 
capacity and particle size distribution of raw water, the action of 
metallic hydrolysis products as "binders," and the occurrence of peri- 
kinetic coagulation. 

In 1958, Pilipovich, Black, and others examined the relation- 
ships among pH, zeta potential, base exchange capacity, coagulant 
dosage, and turbidity removal for the coagulation of suspensions of 
five clays with alum. Clays of high base exchange capacity required 
considerably larger doses of coagulant to accomplish coagulation than 
did clays of lower base exchange capacity. The authors reaffirmed the 
superior effectiveness of hydrolysis products over that of trivalent 
aluminum ions as coagulating agents. 

Matijevic and others ' (19&0 coagulated lyophobic colloidal 



- 8 - 
.. suspensions of known particle charge and concentration -with aluminum 
nitrate to determine the nature of the species formed during alum floe 
formation. Results indicated that below pH 4 the simple trivalent 
hydrated aluminum ion prevails. Between pH 4 and pH 7 the probable 
prevailing complex is the tetravalent Alg((H)«t. At higher pH values 
the tetravalent hydrate is transformed into a divalent form which in 
turn yields to a complex of zero charge. 

In the same year Black and Hannah, using alum and various poly- 
electrolyte coagulants and coagulant aids, investigated the relation- 
ships among pH, electrophoretic mobility, base exchange capacity, coagu- 
lant dosage, and turbidity removal for the coagulation of three dif- 
ferent clay suspensions. Several equivalents of coagulant per equiva- 
l§nt of clay base exchange capacity werg necessary to effect satisfac- 
tory coagulation. The pH range of best coagulation was 7.5 to 8.5 in 
which range the electrophoretic mobilities of the clay particles was 
slightly negative. In some cases fair perikLnetic coagulation occurred 
at pH values less than 4.5. 

In his study of the precipitation of aluminum hydroxide resulting 
from addition of alum to solutions containing bicarbonate, carbonate, 
or chloride of sodium, Packham (i960) evaluated the degree of pre- 
cipitation by measuring soluble aluminum residuals and by photometrically 
recording turbidity of the system as a function of time. The maximum 
amount of precipitate was formed in the pH range 5.5 to 7.2. Maximum 
coagulation rate occurred between pH 7.2 and 7.6, and maximum immediate 
precipitation was observed at pH 7.1 or 7.2. 

As his criterion of coagulation effectiveness, Packham chose the 
coagulant dosage required to reduce the initial turbidity by one-half 



-• 



- 9 - 

for a given set of conditions. The pH range he observed for optimum 
coagulation conditions based upon the use of this criterion does not 
agree with the pH range for good coagulation which others have reported. 
The difference results from the selection of different coagulation 
efficiency criteria. Use of Packham's criterion to select conditions 
for coagulation in a treatment plant -would result in -water of -unsatis- 
factory quality. If he had chosen a much greater turbidity removal 
efficiency as his criterion, his prediction of optimum coagulation pH 
range would have coincided -with those commonly reported. 

Packham expressed the opinion that the coagulation of clay is 
principally accomplished by the enmeshment of the clay particles in the 
metallic hydroxide precipitate formed by reaction of the coagulants. 
Orthokinetie coagulation is the term now used to name the mechanism 

he described. 

20 

Mackrle J (1962) has presented arguments favoring the acceptance 

of the physical theory of stability and coagulation of colloidal clay 
suspensions. He has attached greater significance to the value of the 
psi potential, the potential difference between the "Helmholtz layer" 
and the bulk of the suspending medium, than to the value of the zeta 
potential, the potential difference between the plane of shear and the 
bulk of the suspending medium. He has suggested that the metallic 
coagulants react to form crystalline hydrous oxide sols which de- 
stabilize the clay suspension by mutual coagulation. His conclusions 
were based upon his work with ferric sulfate and clay suspensions and 
upon crystallo graphic studies of such precipitates reported by others. 
In his tests pH and coagulant dose were allowed to vary simultaneously, 
and no measurements of electrophoretic mobility were performed to 



- 10 - 

permit an examination of the independent relationships among pH, coagu- 
lant dosage, turbidity removal and zeta potential. 

In 1962 Stumm and Morgan- 5 cited the work of others and identi- 
fied, for both iron and aluminum salts, the hydrolysis products of 
highest effective charge and assigned tentative formulae to them. They 
also called attention to the aging effect of iron and aluminum sols and 
emphasized the chemical nature of particle charge caused by ionization 
as contrasted with charge produced by physical adsorption. The majority 
of their laboratory tests were performed to determine the specific 
chemical interaction between various functional groups normally found 
in water and the metallic .coagulants in common use. They concluded that 
metallic complexes other than hydrous oxides can be formed as a result 
of th© interactions and that the interaction of the functional groups 
can appreciably affect the pH at which optimum conditions of coagulation 
occur. They also presented a method for carrying out laboratory jar 
tests at constant pH and convincingly justified the desirability of 
such a procedure. 






III. COAGULATION THEORY 

Any explanation of coagulation theory must be preceded by a de- 
scription of the physical and chemical characteristics of the colloidal 
suspensions to be coagulated. The suspensions customarily encountered 
in the treatment of water for municipal and industrial use are dilute. 
Even where raw water is taken from streams which carry heavy sediment 
loads, the water to be coagulated is dilute because presedimentation is 
■used to remove the readily settleable particles. The materials which 
are removed from the dilute suspensions by coagulation can be generally 
classified as turbidity or "color." 

In their study of the nature of colored surface waters Black and 
Christman^ have ascertained that "the materials responsible for color 
in water exist primarily in colloidal suspension in the water." They 
found particle size and number of particles to vary with pH, but particle 
size was generally less than 10 mu-. Although the present research is 
not directly concerned with coagulation for color removal, color com- 
pounds do merit mention, because their colloidal nature and suscepti- 
bility to coagulation are similar to those of colloidal turbidity 
particles. 

The primary source of turbidity to which the present investiga- 
tion pertains is colloidal clay. Clays are complex aluminum silicates 
of sedimentary origin. Their lattice structures consist of layers of 
silicon-oxygen sheets and aluminum-oxygen sheets. These sheets, common 
to all clays, occur in different orders in the different classes of clays. 

- 11 - 



- 12 - 
Kaolinte, montmorillonite, and fuller's earth have been used in the 
present research. 

An important physico-chemical characteristic of clays which is 
considerably affected by the placement order of the sheets is base 
exchange capacity. Kaolinite and montmorillonite, of the clays used in 
the present research, represent the low and high extremes of base 
exchange capacity which results from crystalline structure. 

Kaolinite consists of an alumina sheet and a silica sheet which 
are combined to form one layer, whereas montmorillonite has an alumina 
sheet included between two silica sheets to form one layer. These 
layers have a definite thickness, measurable by x-ray diffraction 
methods, which is constant for a specific clay; but the lattices extend 
to the irregularly broken edges of the crystals in the other tw> direc- 
tions. In water the parallel layers tend to split apart and become 
dispersed. Because of the small coulombic forces between similar 
adjacent silica sheets in montmorillonite, the surfaces of the layers 
become hydrated and therefore separate to a considerable extent. 
Kaolinite layers are held together tightly by hydrogen bonding between 
hydroxide ions on the bottom of one layer and oxygen ions on top of the 
next layer and thus resist separation. A more detailed discussion of 
clay structure is given by Hendricks.-^ 2 

Marshall and KrinbilT 5 - 3 have stated one of the results of the 
structural differences between kaolinite and montmorillonite. The base 
exchange capacity of kaolinite varies with particle size, whereas the 
base exchange capacity of montmorillonite is almost independent of 
particle size. 

Particle size is the property upon which the definition of 






- 13 - 
colloids is based, but colloid behavior results from phenomena involving 
the tremendous surface area inherent in particles of colloidal size. An 
example of the importance of surface phenomena is that the classifica- 
tions of colloids, lyophilic and lyophobic, result from such a phenom- 
enon. Distinction between the two classes depends upon the wettability 
of the surface of the particle. The particles possessing poorly wettable 
surfaces are called lyophobic. Lyophobic colloids are unstable, because 
by coalescing they offer a smaller surface area at which a solid-to- 
liquid interface must be formed. Since the smaller interface results 
in a lower surface energy state and a lower total energy state for the 
system, the coalescence is spontaneous. 

Lyophilic colloids, on the other hand, are stable because of the 
attraction of the (surface for the solvent -- the wettability of the 
surface. These lyophilic colloidal solids which exhibit surface inter- 
action with the solvent are, therefore, the colloids of primary concern 
to water chemists. 

Another surface phenomenon which greatly influences the properties 
of a suspensoid is the electrical charge possessed by the particles. 
The charge can be initiated by several different surface mechanisms; 
still other surface phenomena affect charge magnitude and sign. 

Of the several mechanisms which can produce particle charge, we 
shall first consider the process that might be termed preferential 
ionization. As an example of this mechanism, we shall consider minute 
crystals of silver iodide in equilibrium with a saturated solution in 
which the ionic concentration product is roughly 10" . The force with 
which the two ions are held in the lattice differ greatly. Despite its 
larger size, the more polarizable iodide ion is held much more 



- 3A - 

forcefully than is the silver ion. When the concentrations of the two 
ions in the solution are equal, more silver ions escape into the solu- 

: 

tion than do iodide ions; hence, the crystals are negatively charged. 
If the silver ion concentration is increased, the charge can be reduced 
to zero; a further increase of silver ion concentration can cause a 
charge reversal. 

Ionization of functional groups which are connected to the 
particle by covalent bonds is a second and important source of particle 
charge. Examples of particles thus charged are proteins and ion 
exchange materials. Proteins are formed by long chains of amino acids 
joined by peptide linkages. Some of these amino acids carry an ad- 
ditional carboxyl or amino group which can remain free and exposed to 

m + 

the solvent. Thus they can form COO and M„ ions which are covalently 

attached to the particle. The ion exchange materials are porous solids 

which have built-in acids or basic groups. The natural zeolites and 

many clays are included in this general category. 

Among the other mechanisms which can cause particle charge are 

chemisorption and adsorption of specific ions resulting from van der 

Waal's forces. For particles which are charged by the adsorption of 



specific ions, the surface charge density is greatly affected by concen- 
tration changes of those ions in the solution. 

In all of the mechanisms mentioned above, particle charge was 
achieved by the separation of unlike charges (the destruction of 
electroneutrality ) . Because of the large amount of energy involved in 
the separation of these charges, electroneutrality is disturbed only on 
the ultramicroscopic scale. When any one, or a combination of these 
mechanisms, produces an excess of charges of one sign in any locality, 



- 15 - 
there must exist an equal excess of charges of opposite sign in the 
immediate vicinity. Thus, we find surrounding and very near each 
charged particle an excess concentration of ions of counter sign. 
These ions are called counterions or gegenions. The counterion excess 
occurs only in the solution very closely surrounding each charged 
particle. Throughout the rest of the suspending medium electro- 
neutrality prevails. 

When we speak of electroneutrality and areas of excess charge, 
we implicitly assume that the conditions we describe are the averages, 
with respect to time and space, of the several dynamic equilibria which 
prevail. Brownian movement is one spatial equilibrium which must be 
averaged. Ion exchange is a physico-chemical equilibrium of consider- 
able affect, Each of the equilibria, ineluding these two, eaus© 
fluctuations with respect to time. 

Based upon these averaged conditions, several models have been 
proposed to explain the possible arrangement of the charged surface and 
its surrounding array of counterions. These models have been used by 
chemists, physicists, and mathematicians as bases for their computation 
of theoretical values of parameters for many colloid systems. Probably 
none of the models proposed is correct, but each has been useful in 
the explanation of some observed phenomenon. 

The simplest of these was proposed by Helmholtz. 34 Fig. 1 is a 
schematic section which shows the charged surface and the surrounding 
medium. By ionization or some other mechanism, the surface of the 
particle is charged. This excess of negative charge in or on the sur- 
face attracts toward the surface the positive ions in the solution. 
Helmholtz proposed a model in which all of the counterions so attracted 



- 16 - 



CHARGED 
SURFACE- 



PARTICLE 



r-HELMHOLTZ LAYER OF COUNTERIONS 



L+l 














© .©' 

-SURFACE OF SHEAR 

©•-■-: .'©:■■..- 



BOUND 
SOLVENT 











© 







/a 



©5 ; BULK OF 
V ; y SOLUTION 



< 



h- 
O 

a. 



DISTANCE 



FIG. 1 "-THE HELMHOLT.Z LAYER MODEL 



- 17 - 
are located in a single surface parallel to and very near the surface 
of the particle. His model is analogous to a parallel plate condenser. 
The graph of potential in Fig. 1 represents the potential difference 
between the bulk of the solution and the point within the solid-liquid 
interface that corresponds with the abscissa. 

Fig. 2 depicts the Gouy-Chapman 35 model which is named for the 
two scientists who first considered it in detail. They recognized the 
Helmholtz assumption to be an oversimplification of the spatial 
arrangement of the neutralizing counterions. Reasoning that thermal 
agitation would prevent such an uniform arrangement of gegenions, they 
proposed a diffuse layer of variable but finite thickness which con- 
tains an excess concentration of counterions. In formulating their 
model they also considered the shielding effect of the counterions 
located near the particle upon the attractive force existing between 
the particle and the more distant counterions. The proposed model is 
characterized by a potential versus distance graph, for which the 
potential decreases at a decreasing rate as distance from the surface 
of the colloid increases. 

In addition to the gegenions which are attracted to the particle, 
a sheath of the solvent is tightly bound to lyophilic colloids. This 
sheath is pulled along with the colloid whenever some force such as 
that of gravity causes relative motion between the particle and the 
bulk of the solvent. Thus, there exists surrounding a colloid a surface 
of shear which contains the bound solvent that accompanies the particle 
as it migrates. 

If an electric field is impressed upon a colloid system, the 
colloids migrate toward the pole of opposite charge at a speed 



18 - 



CHARGED 
SURFACE- 



PARTICLE 



GOUY-CHAPMAN DIFFUSE LAYER 
.. — — a 

t ©I ■•> :\. 











© 


















© 
Vx ; ® "'■ r\ ® BULK OF 

^ _ r^> solut| on 

© ' '; 

© : ■;■ ; ;© 

^—SURFACE OF SHEAR 



BOUND 
SOLVENT 



PS! POTENTIAL 




1 ^_z ETA POTENTIAL 

DISTANCE 



FIG. 2 -THE GOUY-CHAPMAN 

DIFFUSE LAYER MODEL 



- 19 - 

proportional to the potential which exists between the surface of shear 
and the bulk of the solvent. (The "bulk of the solvent" refers to the 
portion of the solvent out of the effective interaction range of the 
charged colloids, that is, where electroneutrality occurs on micro as 
well as macro scale.) This shear surface potential upon which the 
velocity of a charged colloid in an electric field depends is called 
the zeta potential, % . The movement of the charged colloid that is 
caused by impression of the electric field is referred to as electro- 
phoresis; and the ratio of particle speed to the intensity of the 
electric field is termed electrophoretic mobility. In units commonly 
used for expression of mobility and potential, a ln/sec/v/cm mobility 
is equivalent to a potential of 13 mv . 

Since the velocity of eolloid movement caused by a measurable 
field intensity can be observed through an ultramicroscope or by 
moving-boundary frontal methods, the electrophoretic mobility of 
colloids is a directly measurable parameter. This parameter is closely 
related to particle charge, surface-charge-density diffuse-layer thick- 
ness, and particle surface potential, which are important parameters 
but are not directly measurable. (The surface potential,}*, mentioned 
above is diagramatically presented in Fig. 2) . 

A model suggested by Stern 36 represents further sophistication 
of the Gouy-Chapman diffuse layer theory. It includes the Stern layer 
of adsorbed counterions which are held in actual contact with the sur- 
face of the colloid. A section of the Stern model and a typical poten- 
tial curve for it appear in Fig. 3. In addition to the zeta potential 
and the surface potential, # , the potential at the interface between 
the Stern layer and the Gouy-Chapman portion of the double diffuse 



- 20 - 



CHARGED 
SURFACE" 



fT 



STERN LAYER 



PARTICLE - 



-3j 










SURFACE OF SHEAR 



© 0: © 
.■;'.©." 
©' ©.© 



BOUND 
SOLVENT 



BULK OF 
SOLUTION 



t 



< 

I— 

Ld 
h- 
O 

% 



Si POTENTIAL-^, 




ZETA POTENTIAL 



DISTANC! 



FIG. 3 -THE STERN LAYER MODEL 



- 21 - 

layer is indicated and represented by the symbol 7^ . ^ 

The models described above are useful as they provide a basis 
for appreciating the phenomena which influence the stability or insta- 
bility of a given colloidal suspension. The primary phenomenon favor- 
ing stability is, of course, the mutually repulsive force between 
similarly charged colloids. 

A particle with its complete double layer is electrically 
neutral, so that it exerts no net coulombic force upon another. This 
situation exists in the case of particles which are sufficiently dis- 
tant from each other. As two particles approach, however, the double 
layers interpenetrate and interact. Should the two particle surfaces 
finally touch, there could be no more diffuse layers between them to 
SQrmn them from the effect of the repulsivt coulombio feroe. It Is 
the work required to thus distort and finally destroy a part of the 
diffuse double layers which causes most of the repulsion. 

Charge density upon the particle surface and concentration of 
ions in the solution surrounding a particle are parameters which 
directly affect stability. Low ionic concentration in the solution 
causes greater thickness of the diffuse layer. High charge density 
results in large psi potential. Thus low ionic concentration and high 
charge density contribute to colloid stability. The relationship of 
these parameters to zeta potential can be seen in Fig. 1. The con- 
ditions which contribute to stability result in high values of zeta 
potential; therefore, zeta potential, or more important, the directly 
measurable electrophoretic mobility can be a useful index of stability. 
A less important phenomenon contributory to stability is the van der 
Waal adsorption of similiions. This occurs to a significant degree 



- 22 - 

only under very specialized conditions, and the effect is more important 
with similiions of large molecular weight. 

The phenomena which are influential toward instability are much 
more numerous than those causing stability, because the former consist 
of all the phenomena which can impair the effectiveness of the latter. 
Of the instability mechanisms, the two most important are the mutual 
attraction (and coagulation) of oppositely charged colloids and the van 
der Waal attraction. The other mechanisms are of much less direct 
importance, or they effect instability through their influence upon or 
in conjunction with one of the two mechanisms mentioned. 

Van der Waal forces' are always attractive; but because they 
result from dipole interaction, they decrease approximately with the 
third power of the distance between the particles. Thus they are 
effective only when the particles are brought into extreme proximity. 
Coulombic forces between similarly charged colloids oppose their 
approach toward each other with force which decreases roughly with the 
second power of the distance between the particles, so that some other 
force is required to push them close enough together for van der Waal 
forces to prevail. Brownian motion caused by thermal agitation is one 
source of such force. Mechanical agitation of a suspension can 
similarly contribute to -instability. 

Some other factors effect instability by reducing the particle 
charge or potential of the colloids. The concentration of "potential 
determining ions" in the solution exerts a large influence upon this 
parameter. The hydrogen ion concentrations will determine the charge 
density and, hence, the potential of any particle which depends upon 
the ionization of carboxyl or amino groups as its source of charge. 



- 23 - 
The concentration of inert ions in the solvent can affect stability by 
increasing the probability of particle collisions as their number is 
increased and by causing compaction of the diffuse layer. 

Ionic concentration is not the only ionic variable which 
influences stability. The valence and size of the specific ions present 
exert effects upon particle charge and potential. The Schulze-Hardy 
rule is a general statement of the observed phenomena that divalent 
counterions are more potent in the production of instability than mono- 
valent counterions and that trivalent ions are much more powerful coagu- 
lation agents than the divalent counterions are. Ion size and less 
important anomalous characteristics of specific ions influence their 
ability to cause colloid instability as is evidenced by the Hoffmeister 
series in which various anions and cations have been listed in order of 
flocculating power. 

Because of the numerous mechanisms which are responsible for 
de stabilization, the many variables which affect stability, and the 
differing chemical and physical nature of the sundry colloidal particles 
which may be encountered, it is practically impossible to calculate the 
conditions under which satisfactory coagulation of a given colloidal 
suspension will occur. It is desirable, therefore, to examine the 
empirical relationships of the parameters that can be measured so that 
the work involved in cut-and-try coagulation can be reduced. 



IV. PURPOSE AND SCOPE' 

The preceding chapters have reviewed the most significant work 
dealing with water coagulation and have summarized contemporary theories 
concerning the basic mechanisms involved. Because of the complexity i of 
relationships among the numberous variables which affect coagulation, 
many researchers have sought to discover empirical relationships among 
the measurable parameters in order that they might more fully understand 
basic coagulation mechanisms . 

Black and Hannah., Pilipovich and others., Black and Willems, 



>s 



and Black and Christian have pursued such a course in the electro- 

phoretic studies of the coagulation of several colloidal materials with 

39 29 

various coagulants and coagulant aids. Packharrr and Kackrle have 

reported some ferric sulfate coagulation research, but neither of them 
performed electrophoretic studies of coagulation in which the effects 
of coagulant dosage and pH have been separately determined. 

The primary purpose of the present research is to add to the body 
of knowledge resulting from the work of Black, Hannah, Willems, Christ- 
mans and Pilipovich: it will seek to learn the relationships among 
electrophoretic mobility, residual turbidity, coagulant dosage, and 
residual iron content of three clay suspensions resulting from their 
ferric sulfate coagulation. The three clays were chosen so that sus- 
pensions containing equal concentrations of them xrould exhibit low, 
medium, and high base exchange capacities respectively. The literature 
contains no references to work of this nature. 

- Zh - 



-25 - 

Because certain materials and procedures irere utilized, the 
study, in addition to its primary purpose, will allow direct comparison 
of the results of ferric sulfate coagulation with the results of alum 
coagulation of these clays reported by Black and Hannah. Moreover, 
the results of these tests may yield experimental confirmation of coagu- 
lation theories previously presented by others. 

The scope of the work was limited to study of electrophoretic 
mobility, residual turbidity, and residual iron content in the ferric 
sulfate coagulation of suspensions of a low, a medium, and a high base 
exchange capacity clay over the pH range 3 to 10. The ferric sulfate 
dosages were 0, 3, 5, and 5Q mg/l respectively. The procedures 
involved xjere jar tests, residual turbidity and iron determinations, 
and electrophoretic mobility determinations. 



V. EXPERIMENTAL MATERIALS AND PROCEDURES 

The experimental portion of the research consisted of (1) jar 
tests for the ferric sulfate coagulation of three clay suspensions and 
(2) the determination of mobilities for the flocculating colloids in 
those suspensions. Coagulant dosages of 0.0, 3.0, 5.0, and 50 mg/l of 

ferric sulfate were used, and pH was varied over the range 3 to 10. 

Final dissolved iron content, final pH, and initial and final turbidity 

of the jar test suspensions were measured, and pH values of mobility 

samples were determined. 

Materials 

Clays 

The clays used to prepare turbid waters were Kaolinite 4 and 
Montmorillonite 23, obtained from Ward's Natural Science Establishment, 
and fuller's earth, obtained from the Floridin Company. 
Ferric Sulfate 

The ferric sulfate used as coagulant was the commercial grade 
manufactured by the Tennessee Corporation, Atlanta, Georgia. Ferri-Floc 
is the registered trademark by which the manufacturer designates this 
material. The analysis of the particular sample of ferric sulfate used 
appears in Table 1. 



- 26 - 



- 27 - 



TABLE 1 
ANALYSIS OF FERRIC SULFATE USED FOR COAGULATION 



Constituent Per Cent by Weight 



Total Water Soluble Iron 21.50 

Water Soluble Ferrous Iron (Fe++) 0.70 

Water Soluble Ferric Iron (Fe+++) 20.80 

Water Insoluble Matter 2.00 

Free Acid (as H 2 S0 4 ) 2.55 

Moisture 2.51 



- 28 - 



Procedures 



Preparation of Clay Suspensions 

40 
Hannah has given the following description of the clays used 

and of the first steps in their preparation: 

The kaolinite and montmorillonite consisted of large lumps of 
dry clay. These materials were crushed and ground with mortar 
and pestle and were then ball -milled for 24 hours. The fuller's 
earth, which was obtained as a dry powder, was ball-milled for 
24 hours. 

The preparatory efforts of others, described above, were performed 

early in 1959. At that time Hannah determined the base exchange 

capacity of each of the three clays in the manner prescribed in Official 

Methods of Analysis of the Association of Official Agricultural 

4-1 
Chemists . Since their preliminary preparation the dried clays had 

been stored in closed glass containers. With the clays in the condition 

described, the present experiment was begun xtfith the weighing out of 

four 3'75-g aliquants of each clay. Each aliquant, in turn, was mixed 

with 500 ml of demineralized xrater and dispersed by mixing in a Waring 

Blendor for five minutes. The four aliquants of each clay suspension 

were placed in a separate covered beaker and allowed to hydrate for 24 

hours. At the end of the hydration period, each suspension was slowly 

passed through a sodium-cycle, ion-exchange column to replace the 

natural, exchangeable cations of the clay with sodium ions. A glass 

column of 25 mm diameter containing a 12 -inch depth of Nalcite HCR 

cation-exchange resin was used for the ion exchange process, which was 



The Waring Blender is manufactured by Waring Products Company, 
New York, New York. 



- 29 - 
developed by Lewis. Just before the treatment of the three clay sus- 
pensions the resin in each was regenerated with one liter of ten per 
cent KaCl solution. 

Stock suspensions were prepared by diluting each of the three 
suspensions to twenty liters with demineralized water. The three sus- 
pensions were stored in polyethylene carboys. 
Preparation of Ferric Sulfate 

A 2-kg portion of commercial-grade ferric sulfate was taken from 
a 100-lb bag of the material which was supplied by the manufacturer. 
After being mixed thoroughly, the sample was quartered, and 500 g were 
reserved for analysis. Approximately 100 g of the remaining material 
was finely ground with mortar and pestle. Aliquants of 1.000 g were 
weighed out and stored in glass vials having tight-fitting polyethylene 
stoppers. 

Because the hydrolysis reactions of ferric sulfate are dependent 
upon time and concentration, a fresh coagulant solution of the chosen 
concentration was prepared daily. One of the previously weighed 
aliquants was quantitatively transferred to a 200-ml volumetric flask, 
which was then filled to the mark with demineralized water. This par- 
ticular concentration was chosen, because less concentrated solutions 
became cloudy and were found to contain considerable volumes of hydro- 
lyzed material within four hours after the initial mixing. A minimum of 
twenty minutes was allowed for the mixing, which was accomplished with 
a magnetic stirrer. 



- 30 - 



Coagulation Tests 

Sample preparation . After the preparation of the aforementioned 
clay suspensions, approximately six months passed before coagulation 
tests were begun. A high-speed mixer, equipped with a stainless steel 
shaft and propeller, was used to thoroughly mix the suspensions. The 
minimum time of mixing for any suspension was one hour. Mixing was con- 
tinued while 200-ml aliquants were pipetted into 8-oz polyethylene 
bottles. Also, triplicate 25-ml samples of each suspension were 
pipetted into beakers, and residue upon evaporation was determined for 
each in accord with the procedure specified in Standard Methods for the 
Examination of Water and Wastewater . ■* which hereafter will be referred 
to as Standard Methods . To provide an ionic concentration in the sus- 
pensions comparable to those of surface waters, 20 ml of 5.00-g/l sodium 
bicarbonate solution was added to each of the 200-ml suspension aliquants. 
In the final clay suspension samples, diluted as described below, the 
sodium bicarbonate concentration was 50 mg/l. 

In the morning of a typical day of coagulation tests, immediately 
after preparation of the coagulant solution, six of the 8-oz bottles 
containing the desired clay were selected, and their contents were 
quantitatively transferred to separate two-liter volumetric flasks in 
which 500 ml of demineralized water had been placed. Ten ml of chlorine 
solution containing 0.&Q0 g/i f Cl 2 were pipetted into each flask. 
(During chlorine demand tests, that specific quantity had proved suffi- 
cient to satisfy the demand of the suspensions and still to leave about 
1 mg/l of free available chlorine to oxidize the ferrous iron present to 



- 31 - 
the ferric state. Such a prechlorination dosage is common for treatment 
of surface water.) Sufficient amounts of 0.1 N NaOH or HC1 were added 
to the flasks to yield the desired pH of the final suspension, and the 
flasks were filled to the mark with demineralized water. A teflon- 
covered magnetic bar was placed in each flask, and the flask's contents 
were mixed for five minutes with a magnetic stirrer. One-liter gradu- 
ated cylinders were used to transfer half of each flask's contents to 
separate i|-8-oz square jars which were placed on the multiple laboratory 
stirrer (hereafter referred to as the jar test machine). The remaining 
contents of the flasks were retained for mobility determinations. 

Sacculation. The flocculation process was begun by rapidly 
stirring the suspensions while adding the correct coagulant dosage to 
each of the six suspensions. After receiving the coagulant dosages, the 
suspensions were mixed rapidly for 2 minutes and then slowly for 28 
minutes. Next the stirring paddles were removed, and the suspensions 
were allowed to settle for 10 minutes. The rate chosen for rapid mixing 
was 100 rpm. The speed initially selected for slow mixing was 40 rpm, 
but soon after laboratory tests were begun, 5 rpm was adopted for slow 
mixing since it appeared that higher rates might cause disintegration 
of the floccules. 

Promptly at the end of the sedimentation period 250-ml samples 
were drawn from each jar. An apparatus similar to that described by 
Cohen was used to siphon each sample from approximately an inch below 
the surface of the supemant. The settled samples so obtained were 
used for residual turbidity and residual iron determinations. 



anA RJw / h ? six -^ aI > variable-speed stirrer used is a product of Phipps 
ana Bird, Inc., Richmond, Virginia. 



-32- 

In itial and residual turbidity measurements . Turbidity of the 

* 
samples was measured in a Lumetron Model 450 Filter Photometer. The 

procedure recommended by the manufacturer J required the preparai:xon or 
a calibration curve for each of the three clays used. Calibration for 
a single clay involved the preparation of eight to ten suspensions so 
that their turbidities uniformly covered the desired turbidity range. 
The optical density of each suspension was measured in the Lumetron- for 
650-e;i light over a 75-mm path* Also, the turbidity of each of the sus- 
pensions was determined with the Jackson Candle Turbidimeter in the 

,46 
manner set forth in Standard Methods. 

Because coagulation efficiency was to be judged upon the basis of 
turbidity removal, determination of initial turbidities was necessary. 
An average value of initial turbidity for each of the three clay suspen- 
sions x<ias obtained by measuring the initial turbidity of the suspensions 
for the jar tests s in which coagulant dosage was zero. 

Re sidual iron determination, ^ The supernatant samples which were 
obtained in the manner described above were filtered prior to the deter- 
mination of their iron content. A fine, smooth , quantitative filter 
paper if was used. Filtration was necessary, because some of the iron 
present was chemically or physically bound to floe particles of such 
small size that they did not settle ou"c in the short settling period 
allowed. In a water treatment plant the iron bound to such small 



*The Lumetron Photometer is a product of Photovolt Corp., New 
York, Hew York. 

*The paper used was paper No. 13061 manufactured by Will Corp., 
New Tork 52, New York. 



- 33 - 

floccules would not be found in the finished water, because sedimenta- 
tion of longer duration or passage through the rapid sand filter would 
remove them. Filtration of the iron samples thus makes the laboratory- 
jar tests more nearly analogous to plant conditions. The iron content 
of several samples was determined without prior filtration. In a later 
chapter results of these determinations are identified and are compared 
with results for similar filtered samples. The variance of iron content 
between the two kinds of samples emphasizes the necessity for filtration. 

The phenanthroline method appearing in Standard Methods y was 
followed for the iron determinations. A 530-mU filter and a 75-mm light 
path were chosen for the Lumetron Model ^50 Filter Photometer used for 
the colorimetric iron determinations. 

Measurement of pH . The final pH of the coagulated clay- suspen- 
sions was measured with a Beckman Model G pH meter. 

Electrophoretic Mobility. Determinations 

Dosing and mixing. A period of four to eight hours usually 
elapsed after the final dilution of the clay suspensions before 
mobility determinations were made. In order to attain thoroughly mixed 
suspensions after the quiescent period, each suspension was stirred for 
five minutes on a magnetic stirrer just prior to the mobility deter- 
minations. The individual suspensions were dosed with the appropriate 
amounts of coagulant at the beginning of the mixing. 



The Model G is a product of Beckman Instruments, Inc., Fullerton, 

California . 



Co n d uc tance measurement . Specific conductance was determined by 
the procedure described in Standard .. Methods . A Model RC16B1 Conduc- 
tivity Bridge with a pipette-form conductivity cell having a cell con- 
stant of i cm""" was used for the measurements* 

Measurement of pH . The pH of each suspension was measured im- 
mediately before the mobility of its particles was determined. A Beck- 
man Model G pH Meter was used for these measurements. 

£a r t icle.mobility_ measurement . The equipment and procedures used 
for the microelectrophoretic mobility determinations are those described 
in the paper by Black and Smith. '° The detailed description of the 
physical dimensions and construction methods for the glass cell appear 
in an article by Briggs, who designed it and for whom it is named. 
Since both procedure and equipment are described in detail in the refer- 
ences cited, only a general discussion of them will be included here. 
In addition to the general account, however , any deviation from the 
suggested methods of Black and Smith will be delineated specifically. 

The Briggs cell is constructed of Pyre:/ glass. Its rectangular 
cross-sectional shape and area are practically constant over the central 
portion of its longitudinal axis. A filling funnel is located at one 
end, and removable electrodes and outlet stopcocks are connected to 
either end of the cell. It is mounted in a metal stand which holds it 
in proper position on the microscope stage and supports it when it is 
not in use. Fig. 4 is Tanbo's sketch^ 1 of a Briggs cell. 



* 

The Conductivity Bridge is a product of Industrial Instruments, 
inc., Cedar Grove, New Jersey. 

' f Pyrex is a product of the Corning Glass Company, Midland, 
Michigan. 



- 35 - 




_J 

_J 
Ll! 

(J 

00 

O 

a: 

DQ 
UJ 



i 

Ll 



-36 - 

Two Briggs cells were assembled, mounted, and calibrated before 
jar tests and mobility determinations were begun. Plastic Wood was 
found to be a more satisfactory packing material than any previously 
tried. If removal from the holder is ever necessary, the cell can be 
freed easily by soaking the assembly in acetone or a similar solvent. 

During the course of this study several improvements in technique 
were developed. (1) The cell holder was attached to the microscope 
stage with a pair of small clamps. This procedure prevented accidental 
misalignment of the cell during determinations. (2) Another deviation 
from the suggested procedure was the use of a 4-rara glass bead in each 
of the electrodes to prevent rapid mixing of the mercuric nitrate and 
potassium nitrate solutions in the electrode. This procedure was pro- 
posed by Briggs. (3) It was found that the mercuric nitrate solution 
could be introduced into the electrode most easily with a hypodermic 
syringe fitted with a 2-in needle. (4) When sufficient mercuric nitrate 
solution was injected to bring the liquid level about 3 mm above the 
narrowest portion of the opening between the upper and lower chambers 
of the electrode, no trouble was experienced in placing the glass bead 
without entrapment of air bubbles beneath it. 

Serendipitously it was discovered that for the suspensions 
studied, electrodes prepared in the manner described above could be used 
over periods as long as a week. Moreover, for these particular suspen- 
sions it was possible to rinse the cell by passing demineralized water 
through it while it remained clamped in place on the microscope stage p 
The application of a low-intensity vacuum to the outlet tube caused 



* 
Plastic Wood is a product of Boyle-Midway, Chamblee, Georgia. 

/ 



- 37 - 

water velocity of sufficient magnitude to remove the settled floccules; 
therefore, it was not necessary to remove the cell from the microscope 
stage more often than once a week. Once the system was aligned and the 
cell clamped securely in place, a check was necessary only at the begin- 
ning and ending of each day's determinations to be sure that the micro- 
scope was focused on the stationary layer inside the cell. The water 
aspirator which was used to pull cleaning water through the cell was 
also useful as an aid in filling the cell with a suspension without the 
entrapment of bubbles. 

The particle velocities were determined by visual observation 
and were timed with a stopwatch. A previously calibrated occular 
micrometer located in the plane of the microscope image of the station- 
ary layer served as the measured course over which the flight of the 
particles were timed. The polarity of the electrodes was alternated 
between individual timings. Thus, of the twenty particles timed for 
each suspension, ten were observed to move toward the left, and ten 
moved toward the right. An exception to this characteristic movement 
was noted at the isoelectric point. At the isoelectric point various 
particles were observed simultaneously to move very slowly toward 
either electrode. The mobility of the particles of a suspension was 
computed from the mean of the time observed for each particle to travel 
a fixed distance; therefore, the computed mobilities are time-averaged 
rather than velocity-averaged mobilities. 



JxouUJDi.ua] >Jt 



Some physical characteristics of the clays which were used and 
tha procedures for preparation of the suspensions studied have been 
described in preceding sections. Table 2 presents the turbidities , 
gravimetric concentrations s and base exchange capacities of these 



i Li L*c* '■ ■ OX1S 



TAJdUi 2 



rxuJiJSttiliio (js Laii GL&z SUSirEHSIQfilS 



litial 



Base Exchange Base Exchange 
Residue Upon Capacity of Capacity of 



oaay 



Turbidity mg/l 



Evaporation Clays 



»eq/ . 



Suspensions 
P-eq/l 



Hcntraorillcnite 58 
Fuller's Earth 79 

Saolinite 294 



62.0 



04" .O 



74.0 



1,150 



265 



87 



71.3 



6.4 



f-iicroequivalents will be abbreviated j^eq. 



The base exchange capacities are important in relation to coagu 
lant dosages. Also, the effects of coagulant dosage upon raobility and 
coagulation in the present study will be compared with similar effects 
of coagulant dos_ge in the alum coagulation study reported by Harm 
It is desirables therefore, that the coagulant dosages used in both 



ah. 



- jo 



- 39 - 
investigations be expressed In terras comparable to the units of base 
exchange capacity employed herein. These expressions appear In Table J, 

TABLE 3 
COAGULANT DOSAGES ■ 



Ferric Sulfat e Alum 

mg/ 1 (ieq/l mg/1 ~TecJl 



3,0 34 5«0 45 

5.0 57 15.0 135 

50.0 570 . 100.0 900 

Although nominal dosages of 5-0 mg/l were included in both 
studies s the effective dosage of aluminum ion Is considerably smaller 
than that of the ferric ion because water of hydration constitutes a 
larger portion of the alum dosage. Probably the most meaningful compari- 
sons between the two investigations can be made for dosages of (1) 5.0 
mg/l of alum ana 3^0 rag/l of ferric sulfate, (2) 5*0 rr.g/l of alum and 
5.0 mg/1 of ferric sulfate , and (3) 100 mg/l of alum and 50 mg/l of 
ferric sulfate. These combinations of dosages are not equal, but the 
two lower ferric sulfate concentrations bracket the lower alum dosage 4 
and the highest dosages of the two studies represent concentrations 
greatly In excess of those necessary for good coagulation. 

The choice of a satisfactory criterion of good coagulation is 
particularly difficult. Adequate coagulation must result in an ex- 
tremely high degree of turbidity removal. The optical property s turbid- 
ity, must be relied upon as an index of removal efficiency. Use of this 



property is complicated by the effects of shape s size, number and refrac- 
tive index of the particles responsible for the turbidity in a given 
sample . 

An example of the manifestation of these effects has been pre- 
sented in Table 2 , The suspensions contain equal gravimetric concentra- 
tions of the three clays, but the turbidities they exhibit are widely 
divergent. For water treatment plant operation a practical criterion 
commonly used requires that the turbidity of coagulated and settled 
water be five units or less. Such a criterion is probably too stringent 
for use in this study because the short period of sedimentation xv T as 
insufficient for the settling of the smaller particles which contribute 
most to the turbidity of a suspension. Moreover, the selection of a 
specific residual turbidity as the criterion would be to require a much 
larger removal efficiency for the kaoiinite suspension (initial turbidity: 
29k units) than for the nontmorillonite (initial' turbidity: 53 units) . 

op 

Packhara has arbitrarily chosen as his coagulation criterion 
that dosage which reduces initial turbidity by 50 per cent. This choice 
is undesirable, because it differs so widely from acceptable conditions 
encountered in water treatment plant operation. Vie have arbitrarily 
chosen 90 per cent removal of initial turbidity as the criterion of 
satisfactory coagulation and results of the two studies will be compared 
on this basis. 

The residual turbidities and particle mobilities for each permu- 
tation of clay and coagulant dosage have been graphed as functions of 
pH. Both graphs for a single permutation appear in the same figure, 
(The residual turbidities are expressed as percentages of the initial 
turbidity of each suspension.) Figares 5 5 6j 7 S and 8 are based upon 






- 41 - 

the turbidity and mobility results for the montmorillonite suspensions 
which were treated with t 3, 5 S and 50 mg/l of ferric sulfate respec- 
tively. 

In Fig. 5 s pH is observed to exert minor influence upon mont- 
morillonite mobility in the absence of any coagulant. Final turbidity 
is little affected by pH. Some turbidity removal was accomplished by 
the agitation and sedimentation of the jar test procedure, but the 

clarification so achieved was not significant. 

40 
Hannah's electrophoretic studies revealed that the mobility of 

the suspended clay alone was relatively independent of pH, but the magni- 
tude of the mobilities he reported were approximately 30 per cent smaller 
than those recorded during the present investigation. The latter agree 

much more closely with the maximum negative clay mobilities reported oy 

20 

Mattson and by others than do Hannah 2 s„ Such agreement can not be 

interpreted to be a proof of accuracy,, because Mattson, for example, 
worked with a different clay and did not report pH values. However, as 
consideration of figures below will indicates the graph of the mobility 
versus pH for zero coagulant dosage does fairly well define the maximum 
negative mobilities observable for the suspensions and coagulant under 
consideration. In view of this relationships comparison of mobilities 
for zero coagulant dosage with Mattson 8 s maximum negative clay mobili- 
ties appears to be worthwhile, 

The lack of agreement with Hannah's values led to a reconsidera- 
tion of the equipment and procedure for mobility measurement. Of the 
mechanical devices which are used, the ammeter is the unit most probably 
capable of introducing an error of such size and consistency. The pre- 
cision of the meters is about one or two per cent of the full scale 



-42- 



■■" 




~ 23456 
*f 120| 1 r — i r 



JO 



>. 100 

5 80 



cr 60 

j 40 

< 

q 20 

c/) 

LU 



7 8 9 10 11 

120 




SLOW MIXING: 

40 RPM -Q-D- 

5 RPM -o-o- 



100 
80 
60 
40 
20 




2 3 4 5 6 7 8 



10 11 



FSG. 5. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 
CLAY: MONTMORILLONITE FERRIC 
SULFATE DOSAGE: 0.0 MG / L 



- 43 - 
readings an d the accuracy is not likely to be as good as the precision. 
When conditions such as the electrolyte conductivity or the available 
power supply voltage make it necessary to measure a current correspond- 
ing to only ten or fifteen per cent of the full scale reading , the error 
involved in the determination may be six to ten times as large as that 
for a reading at full scale. Perhaps the use of some more sensitive 
method of field intensity measurement circuitry would allow closer 
agreement among the results of independent investigators. 

Fig. 6 shows the effect of pH upon mobility and turbidity removal 
of the montmorillonite clay suspension for the 3~ ri1 -g*/l coagulant dosage. 
Increasing pH was accompanied by a gradual increase in the magnitude of 
the negative mobility. The same trend was shown for Hannah's 5-sig/l 
dosage., and, as was previously mentioned, the magnitudes of the mobili- 
ties were only about 75 per cent of those from the present study. Where- 
as the only good coagulation resulting from that alum dose was peri- 
kinetic coagulation at pH less than 4.5, 3-mg/l of ferric sulfate 
yielded good coagulation from pH 5 «5 to pH 5.6. 

With an increase of ferric sulfate to 5 mg/1 as shown in Fig. 7» 
the increase in mobility with increasing pH becomes greater, although 
the curve is not so smooth. The most noticeable effect of the increased 
coagulant dose is the broadening of the zone of good coagulation over 
the range pK 4.6 to 7.8. 

The 50-mg/l ferric sulfate dosage resulted in change reversal 
for values of pH less than 5o* -to Fig. 8 9 the algebraic decrease in 
mobility with increasing pH was observed again as it had been in the 
previous figures , Hannah 9 s comparable alum dose of 100 mg/l resulted 
in a mobility curve of similar shape above pH 4.7 s but the isoelectric 



• 



- l&m 




6 7 8 9 10 11 
pH 

FIG. 6. -THE EFFECT OF pH AND 
MOBILITY UPON COAGULATION 
CLAY: MONTMORILLONITE FERRIC 
SULFATE DOSAGE: 3.0 MG / L 



«*5- 



23456789 10 11 







10 11 
.120 



SLOW MIXING: 

40 RPM -o-o- 

5 RPM -o— o- 




100 
H80 
60 
40 
20 




9 10 11 



FIG. 7 -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 
CLAY: MONTMORILLONITE FERRIC 
SULFATE DOSAGE: 5.0 MG / L 



- 46 - 




> 100|- 

8— 

Q 80 



a 60 

13 
H 

40 



9 10 11 

120 



SLOW MIXING: 

40 RPM -O-D- 

5 RPM -o-o- 



Q 




5 6 7 8 9 10 11 



2 



FIG. 8. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 
C LAY : MONTMORILLONITE FERRIC 
SULFATE DOSAGE: 50. MG / L 



100 
80 
60 
40 
20 




-ap- 
point (pH 6.6) was considerably higher, and below pH k*& as the solu- 
bility of aluminum increased the charge reversal effect of the alum also 
decreased. The alum dose resulted in good perikinetic coagulation be- 
low pH 4.5 and both alum and ferric sulfate produced good orthokinetic 
coagulation from pH 5*5 to 8.8 and from 5.5 to 10.0 respectively. 

Fig. 9 is a composite of the four preceding figures. It allows 
ready comparison of the broadening of the zone of good coagulation with 
increasing coagulant dosage. Also the zone of perikinetic coagulation 
below pH 3.7 and the zone of poor or no coagalation from roughly pH k to 
pH 5 are easily identified. Probably the most important relationship 
graphically illustrated in, the figure is that the isoelectric point 
occuring at pK 5. 3 for the one dosage causing charge reversal marks the 
beginning of the pH zone of most economical coagulation of the particu- 
lar clay and for the arbitrary good coagulation criterion chosen. 

The next series of figures pertain to the coagulation of fuller* s 
earth. Fig. 10 illustrates the effect of pH in the absence of coagu- 
lant. As was the case with mcntmorillonite , in the absence of coagu- 
lant, negative mobility increased with increasing pH value. Perikinetic 
coagulation oc cured below pH 4.2 although no such coagulation had been 
observed for montmorillonite. 

Beginning with Fig. 11, the mobility curves become more complex 
as the varying effectiveness of the coagulants for charge reversal at 
different values of pH becomes more evident. For the 3-mg/l dosage, the 
original particle charge is reversed over a pH range of slightly more 
than one unit. For this particular dose, comparison of mobility curve 
shapes for ferric and alum coagulation are virtually impossible because 
of lack of similarity. Good ferric coagulation was observed over the 



'-■',- V. ;■ 



- kS - ' 



10 1 1 
1G/L FE 2 SQ4) 3 I " 




Pir* 



o. S. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION 
CLAY.: MONTMORiLLONITE 



- 49 - 





3 4 
t r 



7 8 9 10 11 

120 



D 



Q 




SLOW MIXING: 
40 RPM -D-o- 

5 RPM -o-o- 



3 4 5 




6 7 8 9 10 11 
pH 

FIG. 10. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION 
CLAY: FULLER'S EARTH FERRIC 
SULFATE DOSAGE: 00 MG / L 



-50- 




~ 2 3 4 5 

K 120f— r 



6 7 8 9 10 11 

120 




7 8 9 10 11 



FIG. 11. -THE EFFECT OF pH AND 
MOBILITY UPON COAGULATION 
CLAY: FULLER'S EARTH FERRIC 
SULFATE DOSAGE: 3.0 MG / L 



- 51 - 

pH range 5.6 to 7,3. 

Whan the ferric sulfate dose was increased to 5 mg/l (Fig. 12) 
the zone of charge reversal was increased to 3 pH units, and good coagu- 
lation occurred above pH 5.5. A most interesting effect noted in this 
particular portion of the study is the greater efficiency of 5 rpra slow 
mixing for perikinetic coagulation and the better orthokinetic coagula- 
tion that accompanied the 40 rpm slow mixing. 

The mobility curve for the 50-mg/l ferric sulfate dosage (Fig. 13) 
appears to be typical of excess ferric sulfate dosage for the three 
clays studied. Particles were positive below pH 6.3, were isoelectric 
at that point 5 and became increasingly negative as pH was raised to 10. 
The slope of the curve is steepest immediately above and belox-J the iso- 
tlsetsl® paint whieh si§arly indiaatgg & %§&% of atoiisym stability, 
Hannah's comparable alum curve changes less abruptly at the isoelectric 
point, and the apparent effect of increasing solubility at low pH is 
evident. Ferric coagulation is good above pH 4-. 2. 

The composite graph for fuller's earth (Fig. Ik) clarifies the 
relationship between the isoelectric point of the overdosed suspensions 
and the beginning of the zone of efficient coagulation. As was the case 
for montmorillonite, it appears that the "overdosed isoelectric point" 
does mark that beginning. Also s the broadening of the zone of good 
coagulation with increasing dosage is evidenced. 

Individual mobility and turbidity graphs for the kaolinite clay 
are shown in Fig-ares 15, 16, 17, and 18, and Fig. 19 is the corresponding 
composite. The mobility curves are very similar to those for fuller's 
earth, and the comments above concerning the latter are qualitatively 
applicable. Regarding coagulation, the kaolinite is much more nearly 



-52- 



8 9 10 1 1 

r 




9 10 11 

120 



D D 
D 



SLOW MIXING: 

40 RPM -a— o- 
5 PPM 




3 45 6 78 9 10 11 



100 

-80 

-60 

40 

20 





FIG. 12. -THE EFFECT OF pH AND 
MOBILITY UPON COAGULATION . 
CLAY: FULLER'S EARTH FERRIC 
SULFATE DOSAGE: 5.0 MG / L 



- 53- 



9 10 11 
1 b + 2 




5 6 7 8 



9 10 11 



FIG. 13. -THE EFFECT OF pH AND 
MOBILITY UPON COAGULATION 
CLAY: FULLER'S EARTH FERRIC 
SULFATE DOSAGE: 50. MG / L 



- 5k - 



7 8 9 10 11 

T 




6 7 8 9 10 11 



FIG. 14. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION 

CLAY: FULLER'S EARTH 



- 55 - 




3 



5 6 7 8 




9 10 1 1 

120 



SLOW MIXING: 
40 RPM 
5 RPM 




80 
60 
40 
20 



1 3 • 



5 6 7 



10 11 







FIG. 15. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 



CLAY : KAOLINITE 
SULFATE DOSAGE 



FERRIC 
0.0 MG / L 



» 56 - 




f 120 



7 6 9 10 11 

120 




6 7 8 9 10 11 

pH 

FIG. 16. -THE EFFECT OF p H AND 
MOBILITY UPON COAGULATION . 
CLAY : KAOLINITE FERRIC 

SULFATE DOSAGE : 3.0 M G / L 



- 57 - 



9 10 1 1 




fr 120 



9 10 11 
i 1120 




10 11 



FIG. 17 -THE EFFECT OF pH AND 

MOBILITY UPON COAGULATION . 

CLAY; KAOUNITE FERRIC 

SULFATE DOSAGE: 5.0 MG / L 



-58- 



8 9 10 1 1 

i 1 1 1 + 2 




9 10 11 



FIG. 18. -THE EFFECT OF p 
MOBILITY UPON COAGULATION . 
CLAY : KAOLINITE FERRIC 

SULFATE DOSAGE: 50. MG / L 



59 




r (n l L4 — I S — : I— 5— l» <— l_a - 
t i v — » , I C7, I n I— . I i I s \ 

MOBILITY UPON CO/ 
CLAY : KAOLIN I TE 






HOULA1 I L> ) n . 



- 60 - 
similar to the montmorillonite . Most important, however, is that the 

"overdosed isoelectric point" near pH 6.0 marks the beginning of the 

52 
zone of good coagulation. Black and others have shown that the same 

relationship between the "overdosed isoelectric point" and the zone of 

good coagulation exist for the ferric sulfate coagulation of natural 

colored waters. 

An additional observation of possible importance concerns base 
exchange capacities of the suspensions. There was no observation of 
charge reversal in the present investigation for dosages for which the 
ratio of coagulant dose to base exchange capacity (both expressed in 
Heq/l) was less than 1.0. .Good coagulation occurred for all three 
clays, however, with a dosage of 3 mg/l. For this dose the ratio men- 
tioned above for montmorillonite is 0.^8, for fuller's earth is 2.0, 
and for kaolinite is 50 • Work with ferric sulfate doses in a range 
which would yield ratios near unity should reveal more interesting 
information on charge reversal phenomena. 

The U. S. Public Health Service has set 0.3 mg/l of iron as the 
maximum allowable concentration of that constituent in drinking water. 
In the present research, therefore, determination of the residual iron 
content in the supernatant was necessary in order that suitability of 
the various treatments could be evaluated. The results of the deter- 
mination are graphically presented in Figures 20 through 28. 

The most important information obtained from the iron determina- 
tion was that for all the pH zone of good coagulation, the residual iron 
content is below the maximum allox-rable concentration. Another interest- 
ing observation which is generally applicable for the ferric sulfate 
coagulation of the three clays is that residual iron values are less 



- 61 - 



9 10 11 



3 



2: 

O 



< 

Q 
(/) 

UJ 




9 10 11 



RG.20.-THE EFFECT OF pH ON IRON 
RESIDUAL. CLAY: MONTMORILLONiTE 
FERRIC SULFATE DOSAGE: 3.0 MG/L 



-62- 



_J 

3 

z 

o 



< 

Q 
oo 
in 

LI 



1.4 
1.2 
1.0 
0.8 
0.6 
0.4 

0.2- 



O.O 1 



3 

T 



4 5 6 7 8 9 10 11 



#■ 



FILTERED 
UNFILTERED-*-*- 



%* 



^ 




1.4 
1.2 
1.0 
0.8 
0.6 
0.4 
0.2 



f 00 



9 10 11 



pH 



FIG. 21. -THE EFFECT OF pH ON IRON 
RESIDUAL. CLAY: MONTMORSLLONITE 
FERRIC SULFATE DOSAGE: 5.0 MG/L 



- 6 3 - 



_! 



o 



——■■ J 

< 

Q 
CO 

cZ 



1.4 

1.2 
1.0 
0.8 
0.6 
0.4 
0.2 



2 
r 



- 



O.O 1 - 
2 



3 



4 5 6 7 8 9 10 11 



FILTERED -0 0- 

UNFILTERED -#— *- 




# 



1.4 

-11.2 
1.0 
0.8 
0.6 
0.4 



3 4 5 




9 10 11 



pH 



FIG. 22. -THE EFFECT OF pH ON IRON 
RESIDUAL. CLAY: MONTMORILLONITE 
FERR!C SULFATE DOSAGE: 50. MG/L 



.. m - 



2 3 4 5 







O 
t 



< 

=> 

LlJ 



1.4r 

i.o[ 

Q8I 

0.6 
0.4 



7 3 9 10 11 



1.4 
1.2 

1.0 
0.8 
■ 0.6 
04 




9 10 11 



pH 



FIG. 23- THE EFFECT OF pH ON IRON 
RESIDUAL. CLAY: FULLER'S EARTH 
FERRIC SULFATE DOSAGE: 3.0 MG/L 



- 65- 





y 









Q 
a: 



a— w^ 



5 6 7 



1.4 
1.2 

.0 



9 10 11 



FILTERED -0 0- 

UNFILTERED -*— #- 



1.4 
1.2 

1.0 
0.8 




\ 



9 10 11 



pH 



FIG. 24. -THE EF 
RESIDUAL. CLAY: 
FERRIC SULFATE 



ECT OF pH ON IRON 

FULLER'S EARTH 
DOSAGE: 5.0 MG/L 



- 66 - 



10 11 



3 

y 






Q 




7 8 9 10 11 



pH 



FIG. 25.- THE EF 
RESIDUAL. CLAY: 
FERRIC SULFATE 



ECT OF 


pH ON IRC 


)N 


FULLER'S EARTH 




DOSAGE 


: 50. MG/L 



- 6?- 



© 






< 

Q 

if) 




2 



3 4 5 6 



9 10 11 



FIG. 26.- THE EFFECT OF pH ON IRON 

RESIDUAL. CLAY: KAOLlNiTE 

FERRIC SULFATE DOSAGE: 3.0 MG/L 



- 68 - 







o 



< 



il: ,..-«- 



1.2 



I. Of 



D£ 



L. 



f> 0.2 



c.;> 



2 



3 4 5 6 7 




9 10 11 
i 1 i1.4 






FILTERED H) 0- 

UNFILTERED -#— #- 



1.2 
11.0 



^ 



* 




0.4 



#• * * J 



0.2 



9 10 11 



pH 



FIG. 27 -THE EFFECT OF 
RESIDUAL. CLAY: KAOLINI 
FERRIC SULFATE DOSAGE 



pH ON IRON 
TE 

5.0 MG/L 



- 69 - 



8 9 10 11 







y 



r'S 



_J 



a 



(Y 




9 10 11 



FIG. 28.- THE EFFECT OF pH ON IRON 

RESIDUAL. CLAY: KAOLINITE 

FERRIC SULFATE' DOSAGE: 50. MG/L 



- 70 - 
than the maximum allowable concentrations in the low pH range down to 
pH 3.8. Furthermore, even at pH 3.0 no supernatant contained more than 
1 mg/1 of iron in solution. These low residual iron values for clay 
coagulation are much lower than those reported for colored water coagu- 
lation. 

Black and others^ have reported residual iron values for com- 
parable coagulant dosages in colored water that are six times as large 
as the largest observed in the present study for the same pH of 3.0. 
At pH values up to k or 5, the ratio was even larger. The difference in 
behavior of the clay and color colloids in this respect point out the 
need for a more thorough understanding of basic coagulation mechanisms. 

For the present research it was necessary to determine whether 
the pH of the samples employed for mobility determinations were identical 
with the pH of the corresponding jar test suspensions. Figures 29 » 3°s 
31, and 32 show the close agreement between the respective pH values. 
Fig* 33 is a composite of the four, which shows the effect of coagulant 
dosage upon the value of pH. It should be remembered that the suspen- 
sions which were used were synthetic preparations containing 5° mg/l of 
sodium bicarbonate. A more poorly buffered solution might not yield 
such agreement between the two. Even with the systems used it was dif- 
ficult to dose the suspensions with the exact quantities of acid or base 
required to obtain evenly spaced mobility and turbidity curve points. 
Only the curves for fuller's earth are shown, since those for the other 
clays were similar. 



- 71 - 



ir% 



1 Oh ' ! 

* | MOBIL! 
1D tTEST J 



SAMPLES 
RS -D— o- 



ES -0-0- 



1.2 
1.0 

0.8 
0.6 
04 
0.2 

0.0 
0.2 




H 



FIG. 29.- QUANTITIES OF ACID 



OR BASE 



REQUIRED FOR pH ADJUSTMENT OF 

FULLER'S EART 



- 72 




2 3 



FIG. 30.- QUANTIT1E 

REQUIRED FOR pH 
FULLER'S EARTH . 



S OF ACID OR BASE 
ADJUSTMENT OF 



7o 
J m 



1.21 



(T t QSh 



b 



Go 

iLl 



MOBILI 

"EST 



b 



> 



I s § 



■H.J 










FIG. 31. 

REQUIRED FOR 
FULLERS EART 



I S iCLO 



S OF ACID" OR BASE 



H ADJUSTMENT OF 



- 74 - 







50. MG/L , 



^o 



«■*# 



© 5? 



FIG. 32. - QUANTITIES OF ACID OR BASE 
REQUIRED FOR pH ADJUSTMENT OF 
FULLER'S .EARTH . 



75 



.2F 



A 



trp-pp»r^ 



•°r 0.0 



D 

B 

r A1 



LxJ 



cr 

LU 

LsJ 





O 

o 
z 



- 3.0 

06h 5 -° 

50. 



_J 




FIG. 33. - QUANTITIES OF ACID 

REQUIRED FOR pH ADJUSTM 
FULLER'S EART 



OR BASE 
ENT OF 



VII . CONCLUSIONS 

In the present investigation, charge reversal at low pH was 
observed for all three clay suspensions when the ratio of coagulant 
dosage to base exchange capacity (both expressed in M-eq/l) exceeded 
three. With increasing pH the mobilities of these suspensions decreased 
until the isoelectric point (in the pH range 5-7) occurred. This 
"overdosed isoelectric point" was found to mark the beginning of the 
zone of efficient orthokinetic coagulation of all three of the suspen- 
sions studied. Such behavior has been reported for the coagulation of 

52 
colored water with ferric sulfate by Black and others. Furthermore, 

an analysis of the results of clay coagulation with alum reported by 

£(,0 

Hannah revealed that the "overdosed isoelectric point" was an indica- 
tor of effective coagulation conditions for those suspensions. 

The base exchange capacities of the suspensions studied were not 
found to be directly or proportionally related to the coagulant dosages 
required to effect satisfactory coagulation 5 but they did significantly 
affect the coagulant dosages required to cause charge reversal at low 
pH. 

For all of the combinations of ferric sulfate dosages and clay 
suspensions studied, it was observed that in the pH zones of good coagu- 
lation the residual iron values were less than the maximum allowed in 
drinking water by the U. S. Public Health Service. Moreover, even at 

low pH the residual iron values xrere less (by a factor of six to ten) 

52 

than those reported by Black and others for the coagulation of colored 

- ?6 - 






APPENDIX 



- 79 



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+> <H 2J 

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05 PL, 

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CM 



WN, 

^3- 






3" -3- 



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■3 1 



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4- 



o 
3t 



CM 

-5" 



ta 

CD 

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co 



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o 



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W -P 

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3 8* 



>5 O 



•P' 

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Q 



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rt O 

►"3 S3 



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un. 



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t£ — 










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d CD 










sa s 











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co 



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en 



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on 



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S3 



cc- 



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cti 

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~ 80 - 






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o--~- 

to 

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-p 

•p. 
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pi 

E-i 



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O "O" 

•H 

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S3 " 



p 

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H -H 



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K -P 

PI 



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(9 



& CvJ 



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Cvj 



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5 £>- 



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g & 






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no 


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CNi 


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p- 


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ON NO 



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BIBLIOGRAPHY 



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lo Publ i e K eai th 5 eryi c e_ . Drinkin g . Water S tandar ds . 1962, Pub* 95°, 
USPKSj Washington, D. C (1962)* 

2, USPHS Drinking Water Standards, 1962, Federal Register (Mar. 6., 
1962), p. 2152. 

3, U. S, Public Health Service, Drinking Water Standards, 19 6l. 
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4, Black, A, P and Hannah, S. A. Electrophoretic Studies of Turbidity 
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(Apr, 196l). 

5. Water Quali ty and Treatment . AWWA, New York, N. I. (2nd ed. , 
T95O). p. 131* 

6. Packham, R, F, The Theory of the Coagulation Process - A Survey 
of the Literature, 2, Coagulation as a Water Treatment Process. 
Prop,, of the.S oCo f o r... Wat er_ Treatment ..and Examination , 11:106 
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7. D'Arcet, F. Note Relative to the Clarification of the Water of 
the Nile and Water in General Which Holds Earthly Substances in 
Suspension. (Articles from French Journals Translated by J. 
Griscom). J. Franklin Inst , , Hen Series, 22:253 (1833). 

8, Jeunet, K, C, M pr.lt .__ S ci , 7>1007 (1865/, 

9. Austen, P. T. and Wilber, F. A. Report of the Purification of 

Drinldng Water by Alum. Annu?! Report .o f the State .Geologist of 
New Je rsey,. .1534 . Trenton {1885). p. 141. 

10. Fuller s G, W. Water Purifi c ation at Louisville . Van Nostrand Co,, 
New York (IS98). 

11. Bull, E, V, Manufacture and Use of Chlorinated Coppers, Proc, of 
Indi ana. Water. ..Supp ly... Assn . (1912). p. 119. 

12. Hedgepeth, L. L. and Olsen, W. C, Chlorinated Copperas - A New 
Coagulant. Jour., AWWA , 20:467 (1928). 

13. Black, A. P. Theory of Coagulation. Water and Sewage Works , 
108:R192-97 (Oct. 1961). 



- 103 - 



- 104 - 

14, fheriault, E,,J. s^d Clark, W. M. An Experimental Study of the 
Relation of H Concentration to the Formation of Floe in Alum 
Solution, Pub. Health Repts ,, 38:181 (1923). 

15, Baylls, J, R. Use of Acids With Alum in Water Purification and 
the Importance of H Ion Concentration, Jour. AWWA, 10:365 (1923). 

16, Miller, L. B„ On the Composition of the Precipitate From Partially 
Alkalinized Alum Solutions. Pub. Health Repts ., 38:1995 (1923). 

17, Miller, L. 3. A Study of the Effects of Anions Upon the Properties 
of Alum Floe Pub a Health Repts, , 40:351 (1925), 

18, Miller, L. B, Some Properties of Iron Compounds and Their 
Relations to Mater Clarification, Pub a . Health Repts , , 40:1413 
(1925). 

19, Bartow, E. and Peterson, B, F. Effect of Salts on the Rate of 
Coagulation and the Optimum Precipitation of Alum Floe, Ind a Eng. 
Chem, 9 20:51 (1928) . 

20, Kattson, S. J. Cataphoresis and the Electrical Neutralization of 
Colloidal Material. J, Phys. Chem., 32:1532 (1928). 



21* Black, A s P., Rice s Owen, and Bartow, Edward, Formation of Floe 
=y 



by Aluminum 'Sulfate, Ind. Eng. Chem ., 25:811 (1933) ■ 



22, Bartow, Edward s Black, A. P., and Sansbury, W. E. Formation of 
Floe by Ferric Coagulants, Ind, Ens:, Chem ., 25:898 (1933); 
Proo. AB.CE, 59:1529 (1933). " 

23, Black, A. P. Coagulation With Iron Compounds. Jour, ..AWWA, 
26:1713 (193^)0 

24, Langeller, W. F. and Ludwig, H, F, Mechanism of Flocculation in 
the Clarification of Turbid Waters. Jour. AWWA , 4l:Io3 (Feb, 1949). 

25, Langeller , W, F. and Ludtdg, H. F, Flocculation Phenomena in 
Turbid Water Clarification, Prop.. ASCB , 78:No. 118 (1952), 

26, Pilipovich, J. B, , et al, Electrophoretic Studies of Water 
Coagulation, Jour., AWWA , 50:146? (Nov. 1958), 

27, Matijevic, E., et al, Detection of Metal Ion Hydrolysis by 
Coagulation, III. Aluminum. J, Phys,,,,, Chem . , 65:826 (1961). 

28, Packham, R. F. The Coagulation Process, III. The Effect of pH 
on the Precipitation of Aluminum Hydroxide. Tech. Paper No... 17_ , 
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29, Mackrle, S, Mechanism of Coagulation in Water Treatment. Jour, of 
the Sanitary Ehg, Liv, ASCE, 88:No. SA3, p. 3U7-1 (May, 1962). 



- 105 - 

30. StunUa W. and Morgan, J. J. Chemical Aspects of Coagulation. 
Jour. AWWA , 54:971 (Aug. 1962). 

31. Black, A. P. and Christman, R. P. Characteristics of Colored 
Surface Waters. Jour. AWWA , 55:753 (Jim, 1963). 

32. Hendricks, S. B. Base Exchange of Crystalline Silicates. Ind. 
Eng. Chem ., 3?:625-30 (1945). 

33. Marshall, C. S. and Krinbill, C. A. The Clays as Colloidal 
Electrolytes. J. Phys. Cheia . , 46:1077-90 (1942). 

3^. Helmholtz, L. F. Ann. , Physik, 7*337 (1879). Has been ' translated. 
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Bull,. No. 33 , University of Michigan, Ann Arbor (1951) • 

35. Mysels, K. J a Introductio n to Colloid Chemistry , Interscience 
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36. Mysels, K. J. Introductio n to Colloid Chemistry , Interscience 
Publishers, New York (1959). P* 330. 

37. Black, A. P. and Willems, D. G. Electrophoretic Studies of 
Coagulation for Removal of Organic Color. Jour., AWWA , 53^589 
(May 19ol). 

38. Black, A. P. and Christmas, E. F. Electrophoretic Studies of 
Sludge Particles Produced in Lime-Soda Softening. Jour. AWWA , 
53^737 (Jim. 1961). 

39. Packham, R. F. The Coagulation Process - A Review of Some Recent 
Investigations. Froc o f the Soc. for Water Treatment and 
Examination , 12:15 (1963) • 

40. Hannah, S. A. Effects of pH and Polyelectrolyte Coagulant Aids 
on Coagulation of Clay Suspensions., M.S. Thesis, Dept. of 
Chemistry, Univ. of Florida, Gainesville, Fla. (i960), p. 24. 

41. Replaceable Bases in Soils Devoid of Carbonates. Ofjj^i^ljfeth^ds 
of Analysis of .the Association of Offic ial Agr icultural Chemists. 
George Banta Publishing Co., Menasha, Wis. (8th ed., 1955)* 

pp. 39-42. 

42. Lewis, D. R, Replacement of Cations of Clay hj Ion Exchange 
Resins. Ind. gng. Chem ., 45 -.1782-3 (1953). 

43. Standard Methods for the Examination of Water and Wastewater. 
APHA, AWWA and WPCF, New York (llth ed. , i960), p. 213. 

44. Cohen, J. M. Improved Jar Test Procedure. Jour. AW^JA, 49:1425 
(Nov. 1957).